1. Field of the Invention
The present invention is a method of and apparatus for inhibiting tissue metabolism in the area of the brain and, more particularly, is a method and apparatus for inducing localized hypothermia and general hypothermia during the emergency treatment of cardiac arrest, severe shock, or systemic hypothermia in the treatment of other medical conditions such as stroke.
2. Description of the Background
Systemic hypothermia can dramatically postpone neurologic deterioration in hypoxic or anoxic tissues. Though initially thought to be due to reduced metabolism, since oxygen reserves are depleted early on in hypothermic cardiac arrest, hypothermic inhibition of triggering events during ischemia and reperfusion injury are now thought to be responsible for hypoxic injury. For example, accidental submersion in cold waters, and the commensurate systemic hypothermia thus produced, has consistently contributed to the neurologic survival of accident victims who otherwise would have sustained irreparable brain damage. Observation of this phenomenon led medical practitioners to induce systemic hypothermia in the course of various hypoxia and anoxia-producing surgical procedures in order to reduce both the systemic metabolism and the associated overall oxygen requirement of the patient.
Whereas systemic hypothermia may be induced with less difficulty in the hospital environment, emergency inducement of systemic hypothermia in a non-hospital setting can be difficult or impossible. As a result, induced systemic hypothermia forms no part of, for example, pre-hospital emergency cardiac care such as cardiopulmonary resuscitation (CPR), notwithstanding the beneficial metabolic inhibition which such hypothermia would provide. Similar emergency procedures in which hypothermia has not been induced to date include the pre-hospital emergency care administered to patients in severe shock or stroke. Cooling after cardiac arrest is being performed by paramedics via haphazard application of cold packs and infusion of cold intravenous fluids. Neither of these techniques have been studied or are necessarily relevant to patients suffering from cardiac arrest and would not be available to typical non-paramedic first responders.
Induced localized hypothermia has been used widely in the non- or pre-hospital treatment of numerous physiologic conditions. Cold packs of some sort are standard equipment in first aid kits, and are used to decrease peripheral blood flow and commensurate swelling in the event of contusion, insect bites or stings, nosebleeds, sprains, etc. Cold compresses to the head, of course, have long been a standard symptom-relieving measure for headaches and fever. In addition to these common treatments, however, three of the less well-known uses for topical cold applications are described in U.S. Pat. Nos. 2,438,643, 3,175,558 and 4,552,149.
U.S. Pat. No. 2,438,643 discloses a pack, for use in local refrigeration anesthesia, which contains a plurality of waterproof compartments which contain brine and an absorbent material, such as sawdust. The pack may be cooled in any suitable refrigerating device and then used as a topical cold pack. Because the pack must be refrigerated, its utility for inducing localized hypothermia is limited to those areas for which refrigeration is available.
U.S. Pat. No. 4,552,149 also discloses a coolant-containing, refrigerant-dependent cold pack which is, more specifically, a head coolant device. The device comprises a main body consisting of a cooling piece for covering the top of the head and a plurality of cooling pieces radially arranged around the main body, for covering the front, sides, and back of the head. This head cooling cap is designed to inhibit hair loss during the administration of a drug or chemotherapeutic agent for which hair loss is a known side effect. As with all cold packs which require refrigeration, the head coolant device is best suited to hospital and home application, and is not well suitable for use in the types of pre-hospital emergency care for which refrigeration is commonly unavailable.
U.S. Pat. No. 3,175,558 discloses a thermal therapeutic pack, specifically designed for postpartum application to the female perineum, which contains the unreacted constituents of endothermic reaction. The unreacted constituents are separated by frangible barriers, time-release capsules, or both, and the separation is maintained until the cold pack is needed. At the time of use, the reactants are admixed by, for example, manually cracking the frangible barrier between them, thus commencing the endothermic reaction and reducing the overall temperature of the cold pack and its contents. The pack is positioned on the patient, as desired, to cool the area of application by the reverse conductive heating of the pack by the body.
In several prior art devices, the cooling of the fluid in the device is accomplished through an endothermic reaction between water and ammonium nitrate which are usually present as a single population of pellets. The amount of reactants and form of the reactants are generally chosen to produce a fluid that does not drop below freezing, where tissue may become frozen and subsequently suffer damage. While avoiding tissue damage, such conditions result in sub-optimal cooling of the patient, thus reducing the beneficial effects of cooling.
As noted above, those prior art patents possess deficiencies, such as requirements for electricity, that preclude their effective use in the emergency treatment of cardiac arrest or severe shock in the field. The inventions disclosed in U.S. Pat. Nos. 4,750,493 and 4,920,963 addressed and overcame those deficiencies. At the same time, the devices disclosed therein were relatively bulky with preferred dimensions of 2′×2′×2′. In combination with their preferred weight (25 pounds), the devices were limited in the areas where could be stored and deployed. Thus, there remains an unaddressed need in the medical community for portable devices with limited physical profiles that provide for inducing controlled hypothermia for cooling of the cranial and extracranial areas. In addition, there remains an unaddressed need for rapid and deep cooling of patients, while at the same time avoiding tissue damage from freezing.